1. Field of the Invention
The present invention relates to an air intake structure of a motorcycle, more particulary to the air intake structure for carrying air from an air intake member to an air cleaner of an engine in a motorcycle.
2. Description of the Related Art
A generally known air intake structure of the engine for a motorcycle has an air intake member disposed at the front end of a body of a motorcycle with its intake opening forward to take in incoming air efficiently and an intake duct for carrying air taken in through the air intake member to an air cleaner. A part of the body frame is used as an intake air passage to reduce the necessary length of the intake duct and space for containing the intake duct.
FIG. 7 is a sectional view in a horizontal plane of a conventional air intake structure and FIG. 8 is an enlarged sectional view taken on the line VIII-VIII in FIG. 7.
Referring to FIG. 7, a body frame 100 of the motorcycle has a hollow head member 102 housing a head pipe 101, and right and left main frame members 105 extending backward from the head member 102 on the right and the left side, respectively, of the body frame 100. The open front end of an air intake duct 106 is connected to the front end of the head member 102. The head member 102 defines a substantially straight, longitudinal intake passage 110.
Referring to FIG. 8, a part of the head member 102 corresponding to the rear end of the intake passage 110 is connected to an inlet duct 115 connected to an air cleaner 112. A resonator 116 for intake noise suppression is connected to the air intake duct 106 so as to project downward from the air intake duct 106. Air taken in through the open front end of the air intake duct 106 flows through the intake passage 110 in the head member 102. The air devides into right and left sides at the head pipe 101 and flows into the air cleaner 112. The air passage between the air intake duct 106 and the air cleaner 112 is substantially straight.
Referring to FIG. 9 showing another conventional air intake structure disclosed in JP-A No. 2001-152990, a body frame has a Y-shaped head box 201 housing a head pipe 200. An air intake duct 203 is joined to the front end of the head box 201. Right and left outlet openings 205 are formed in the back wall of the head box 201. An front openings 211 of an air cleaner case 210 is connected to the outlet openings 205. A water drip plate 213 having the shape of an inverted V is disposed inside the air cleaner case 210 so as to confront the openings 205 and define right and left intake passages 215 connected to right and left air cleaner elements 216.
In the air intake structures shown in FIGS. 7 and 8, since air taken into the air intake duct 106 flows through the substantially straight intake passage 110, the resonator 116 is provided to be connected to the air intake duct 106 so as to project downward from the air intake duct 106 for intake noise suppression. Therefore, the motorcycle needs to provide a space for installing the resonator 116 therein and there is a limit to the volume of the resonator 116. Further water, such as rainwater, leaked into the air intake duct 106 is carried by air flowing at a high velocity into the air cleaner 112. Therefore, the inlet of the air cleaner 112 is opened downward as shown in FIG. 8, and an additional dehydrating mechanism may be necessary on the upstream side of the inlet of the air cleaner 112. Thus, additional work is required for preventing the leakage of water into the air intake structure.
The air intake structure shown in FIG. 9 has the Y-shaped head box 201 defining an air passage sharply expanded toward the main frame members 204 such that the sectional area of the air passage increases rearward to suppress intake noise. In this air intake structure, all the air taken in through the air intake duct 203 flows into the wide Y-shaped part of the air passage and the flow velocity of the air drops sharply, and then the air flows through the right and left outlet openings 205 into the intake passages 215 of the air cleaner 210. Therefore, a satisfactory intake noise suppressing effect is low, and the large drop of the flow velocity of the air reduces intake efficiency. The water drip plate 213 having the shape of an inverted V is disposed inside the air cleaner case 210 to prevent the leakage of water into the air cleaner case 210. Therefore, the volume of a space on the clean side in the air cleaner case 210 is small. It is difficult to prevent the leakage of water into the cleaner case 210 effectively only by the water drip plate 213.